Abstract

We have proposed a new friction test method under severe friction conditions. The method applies backward extrusion, which enables us to create high surface pressure, large surface area expansion and a long sliding distance. In addition, die temperature in the actual forging processes can be reproduced. The unique feature of the die set used in this method is a punch rotating at a very slow angular velocity. From the combination of measured load P and torque M, friction coefficients μ of the entire punch contact surface can be calculated. The equation between M/P and μ was derived using FEM analysis. This equation depends on the punch shape, not the flow stress of material. By this method, we measured friction coefficients at 900 ℃-1200 ℃, in which warm and hot forging conditions of steel were reproduced. As a result, we were able to quantitatively evaluate the lubricant combustion temperature, billet antioxidant coating, lubricant spray pressure, and billet initial temperature, which strongly affect friction coefficients.

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